AGNUS DEI, ("Lamb of God"):
1. An ancient liturgical formula in the celebration of the Eucharist, found in some manuscripts of the Sacramentary of Gregory the Great after the Lord's Prayer and the Libera. The full text, based on John i. 29, is "Agnus Dei, qui tollis peccata mundi, miserere nobis." It is found also in the ancient Eastern hymn which was annexed to the Gloria in Excelsis (see LITURGICAL FORMULAS, II., 3) and was early introduced into the Western Church in Latin translation, where the form is "Domine Fili unigenite, Jesu Christe, Domine Deus, Agnus Dei, Filius Patris, qui tollis peccata mundi, miserere nobis; qui tollis peccata mundi, suscipe deprecationem nostram." When the Second Trullan Council (692) undertook to forbid the representation and invocation of Christ under the figure of the lamb, Pope Sergius I., to express the opposition of the Roman Church, decreed that the Agnus should be sung by priest and people at the Communion. After 767, under Adrian I., it was sung by the choir only. The ritual of the mass, based in this particular on a custom which can be traced to the beginning of the eleventh century, prescribes that the priest, before taking the sacrament, shall recite the Agnus Dei three times, bowing and beating his breast to express contrition for sin, the third time with the addition of "dona nobis pacem." The consecration precedes, the Lord's Prayer is sung with the Libera nos; a piece of the consecrated and broken bread is then thrown into the cup, and the Agnus follows. At the Church festivals it is accompanied with telling effect by soft and tender music. In the mass for the dead the words "give them rest" are substituted for "have mercy upon us," the third time with the addition of "eternal."
The Agnus was accepted in the Evangelical Lutheran Church at the beginning, either in the translation of Nicolaus Decius, "O Lamm Gottes unschuldig," or in the more exact form, "Christe, du Lamm Gottes, der du trägst." In the days of rationalism it was often omitted, or the phrase "Son of God" was substituted for "Lamb of God," the latter being thought to imply an unchristian, Levitical sacrificial conception. It was afterward restored, and is now used in numerous musical settings. In the Church of England the Agnus was incorporated in the Litany, but only to be repeated twice; and the last form (ending with "grant us thy peace") was placed first. In the first prayer book of Edward I. it was included in the communion office, but was omitted in that of 1552 and all subsequent revisions. Nevertheless, it is almost invariably sung by congregations of High-church affiliations.
BIBLIOGRAPHY: H. A. Daniel, Codex liturgicus, vols. i., ii., Leipsic, 1847-48; L. Schöberlein, Schatz des Liturgischen Chor- und Gemeindegesangs, pp. 398 sqq., Göttingen, 1880; G. Rietschel, Lehrbuch der Liturgik, p. 386, Berlin, 1900. Musical settings, by Vittoria, Palestrina, F. Burmeister (1601), F. Decker (1604), M. Prætorius (d. 1621), Mozart, and others; consult R. von Liliencron, Chorordnung, Gütersloh. 1900.
2. Name given to a wax medallion, bearing the figure of a lamb, made from the remains of the paschal taper, and consecrated by the pope in the special ceremonies on the Sunday after Easter in the first year of each pontificate and every seven years thereafter. These medallions are presented to distinguished individuals or to churches, are often enclosed in cases of costly workmanship, and are carefully preserved, almost like relics.